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ADS131M02: 24 Bit RTD Measurement using ADCs that are in stock

tim jager
Prodigy 120 points
Part Number: ADS131M02
Other Parts Discussed in Thread: ADS124S06, ADS131M08, ADS124S08, ADS1248, ADS1247, ADS1261, ADS1260, ADS1220, ADS122C04

TI has some ADCs (such as the ADS124S06) that are very well suited to ratiometrically measuring RTDs (4 wire PT100, or 2 wire PT1000) with great performance (accuracy, precision, noise rejection, etc.). However, these parts have been out of stock for a long time. Could you recommend an alternate solution for measuring RTDs using a chip that is currently available in QTY 20,000+? For example, could the ADS131M02 be made to work and produce measurements with similar performance as the ADS12406?

  • 0
    TI__Mastermind 18900 points

    Hi Tim,

    ADS131M02 probably isn't your best bet, let me see if I can get the expert of the ADS124S06 or ADS1x48 to weigh in. 

    I'm not really an expert with RTD and ratiometric measurements, but from what I know, one of the requirements is to have a range for an external reference. The ADS131M02 has an internal reference so that's not really an option. The ADS131M08 has the option of external reference but it needs to stay very tight around the voltage which also doesn't meet the requirements. 

    Best,

    -Cole

  • 0 in reply to Cole Macias
    TI__Guru** 112935 points

    Hi Tim,

    I'm sorry you are facing supply issues and TI has had many similar requests in recent months.  This means that alternate devices are also suffering supply issues.  Due to the demand TI is working very hard at identifying where supply/demand are critical.  One of the devices we have identified is the ADS124S08 (and ADS124S06) and are improving the flow to get this device out more quickly.  Getting into the purchase queue is the best plan of action.

    Other possible choices are:

    • ADS1247, ADS1248
    • ADS1260, ADS1261
    • ADS1220
    • ADS122C04 (similar to ADS1220 but with I2C interface)

    I would also recommend that you take a look at A Basic Guide to RTD Measurements.  There is also another method for measuring RTD resistance and that is by using a voltage divider circuit where the voltage divider is excited by a stable reference voltage also used by the ADC.  The RTD resistance is determined by taking two measurements (one measurement of the known resistor value and one measurement of the RTD) and determining the RTD resistance by calculation using the known resistor value in the voltage divider.  This method may open up additional ADCs that can be used, but for high levels of precision, many of the same ADCs mentioned above would be used for this method as well.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 120 points

    Hi Bob, thank you for the feedback. It looks like all of the other possible choices you listed are also out of stock. 

  • 0 in reply to tim jager
    TI__Guru** 112935 points

    Hi Tim,

    Sorry for the delayed response as I have been out of the office for the past week and unable to respond.  As I stated earlier, the issues with devices out of stock is a real problem and the best course of action is to place an order.  As I also stated earlier the ADS124S0x devices are the most likely to become available before the others mentioned.

    Best regards,

    Bob B